Rebreather system

ABSTRACT

A semi-closed rebreather that uses a “normal open” type of solenoid valve to control the flow of replenishment gas supplied to the rebreather circuit by at least one replenishment gas cylinder. In the absence of energy, the rebreather system takes the open condition, thereby allowing a replenishment gas flow with a maximum flow rate predetermined during the initial design or adjustment step.

FIELD OF THE INVENTION

The present invention relates to a semi-closed circuit rebreather system.

BACKGROUND OF THE INVENTION

A semi-closed circuit rebreather is a device that allows the diver's exhaled gas to be reused, by filtering the carbon dioxide content and replacing the oxygen metabolized during breathing.

The air around us consists of about 21% oxygen, 78% nitrogen and 1% other gases such as helium, argon and others. To survive, humans must breathe a gas with minimum oxygen content. Not all the breathed oxygen is metabolized and thus consumed during breathing, but that does not mean that you could just breathe a gas containing the amount of oxygen that is then actually metabolized.

Under normal conditions, for example, we inhale 21% oxygen and exhale about 17% (which is why, for example, mouth to mouth breathing can provide the oxygen needed to maintain or restore the basal level of oxygen in the body of a person undergoing cardiopulmonary reanimation), namely we metabolize and then consume only 4% oxygen. But if the oxygen content of the inhaled gas drops below 18%, symptoms such as headaches and other discomforts begin to occur and, below 16%, even more problems begin to occur. A further lowering of the value leads, among other things, to sleepiness, which is followed by death without the person really realizing it.

Under normal conditions, pressures on sea surface are close to 1 bar, so we can consider oxygen as a percentage. But from the physiological point of view it is more correct to talk about partial pressures of oxygen. This type of quantity allows hypobaric environments (high mountains, where the pressure for example can be 0.7 bar at 3000 m altitude) and hyperbaric environments (underwater, where about 1 bar of pressure is added every 10 m of depth) to be considered as well. The partial pressure of a gas is defined as the volumetric fraction of a gas in a mixture multiplied by the pressure of the mixture itself. So 21% oxygen at atmospheric pressure corresponds to about 0.21 bar, where the imprecision is caused by fluctuations in atmospheric pressure due not only to climatic effects but also to altitude.

The human being, under normal conditions (therefore not under stress, where consumption increases) consumes 0.04-0.05 bar of oxygen per respiratory cycle and needs at least 0.18 bar of oxygen partial pressure in the breathed gas in order to metabolize oxygen without having symptoms such as headache or worse.

When the oxygen partial pressure drops below 0.16-0.18 bar, this is considered HYPDXIA or oxygen deficiency. Similarly, we talk about HYPEROXIA when there is too much oxygen. Hypoxia can obviously be lethal, but also hyperoxia can lead to very serious consequences. Depending on the duration of exposure to high-pressure oxygen, the tolerable limit for humans is 1.4-1.6 bar, while the value of 1.3 bar is tolerable even for long exposures and is therefore considered a safe limit.

In traditional diving, the diver carries a cylinder of compressed air that is supplied to the diver at ambient pressure by means of pressure reducers and demand valves (the so-called first and second stage regulators).

Since the ambient pressure increases by 1 bar every 10 m of depth, at 10 m we have 2 bar, at 20 m 3 bar etc. Recalling the definition of partial pressure, at 30 m the diver inhales 4 bar×0.21=0.84 bar of oxygen, but consumes only 0.04 bar as on the sea surface, resulting in still a lot of unused oxygen in the gas exhaled in the form of bubbles coming out from the second stage and rising to the sea surface.

The idea is therefore not to exhale the gas into the surrounding water and disperse it into the environment thereby eliminating it from the breathing system, but to keep this gas in the circuit of the breathing system and make it available to be breathed again thereby exploiting its high oxygen content. The oxygen consumed, i.e. metabolized according to the correct medical definition, is turned into CO₂, carbon dioxide. CO₂ is a gas which, even at very low levels, can have very negative consequences for humans, so breathing the exhaled gas that still has high oxygen content is fine, as long as carbon dioxide is removed. In addition, since the content equivalent to the partial pressure of 0.8 bar of oxygen does not last long, a system to replenish the oxygen consumed must also be provided.

The above concept is the basic concept of a rebreather, which is of two types. In the so-called closed circuit type, the diver has a circuit comprising a CO₂ filtering system, and two separate gas cylinders: one of pure oxygen and one of diluent (usually air). In the semi-closed circuit type, the filtering system is conceptually identical to that of the closed circuit, but there is only one cylinder, containing a mixture of oxygen-enriched air. In both cases the volume of the circuit has to match the maximum volume expected to be exhaled, which is about 51, and which is called “counterlung,” often, but not necessarily, divided into two parts, one before and one after the CO₂ filtering system.

In the closed circuit the metabolized oxygen is replenished by the pure oxygen cylinder, whose flow can be manually or electronically controlled, so as to always have exactly the same volume of gas. This system provides the highest efficiency in the use of gas and allows even very long dives to be carried out, while using very small-volume cylinders. Still talking about the closed circuit, in order to prevent the above mentioned hyperoxia, a cylinder of diluent is absolutely required. For example, if the diver is at 30 m with a partial pressure of oxygen of 1.3 bar, to dive down to 40 m he must “dilute” this oxygen because otherwise the partial pressure of oxygen rises to over 1.6 due to an additional one-bar increase in ambient pressure caused by going from 30 to 40 meters deep.

In the semi-closed circuit, oxygen is replenished by the oxygen-enriched air cylinder, for example 40% oxygen and 60% nitrogen (usually called Nitrox 40 in diving lingo). This type leads to an extreme simplification of the system due to various reasons that are not the object of this patent, but has one drawback: if 4 units of oxygen metabolized in a respiratory cycle have to be replenished then in so doing 6 units of nitrogen are necessarily added as well. This excess volume of gas must be disposed of in the environment because otherwise the counterlung volume increases excessively thereby pushing the diver to the sea surface.

The counterlung is therefore required to have a certain, more or less continuous, gas leakage, from which the name semi-closed originates. This leakage has two obvious drawbacks: the gas lost contains oxygen too, so the system efficiency is lower than that of the closed circuit, and moreover, by using a mixture of oxygen and nitrogen to replenish oxygen, with respect to the gas mixture in the cylinder a fraction of oxygen lower than the starting one will be always obtained.

The advantage relative to the simplicity of the open system with respect to the closed one largely compensates for this drawback. In fact, when a semi-closed system is made, a purely mechanical system can be provided, with an orifice allowing the constant escape of gas without requiring any particular valve, if the flow is sufficient to cover the oxygen demand even in a condition of maximum effort.

However, in order to cover the oxygen demand in emergency conditions, the flow of replenishment gas is still required to be very high and, as a result, the system efficiency is low in terms of breathable gas consumption.

By increasing the complexity, which however is always less than that of a closed system, it is possible to integrate an electronic control system in combination with sensor systems as well as a solenoid valve. The control system provided with the sensors and the solenoid valve monitors the partial pressure and hence the oxygen fraction in the gas, and accordingly opens the solenoid valve that regulates the replenishment gas flow only when the latter is required. Since a minimum amount of oxygen is always metabolized and therefore must be continuously replenished, in parallel with the solenoid valve a replenishment gas flow regulator can be provided, e.g. a passage orifice whose opening is permanently adjusted or can be permanently adjusted. This flow rate regulator of the replenishment gas does not have to be adjusted for an emergency flow, i.e. a flow ensuring the replenishment of metabolized oxygen amounts that exceed a normal mean value, but for a minimum flow just ensuring the replenishment under normal or average oxygen consumption or metabolization conditions. In this system, the solenoid valve has the function of compensating for the fluctuations of partial pressure due to any peaks in oxygen consumption.

Systems of this type are known at the state of the art, but they are designed so that in the absence of power (electricity in the form of batteries powering the various circuits and valves) the control system stops and the oxygen consumed is no longer replenished. As a result, the partial pressure of oxygen drops to the point where the diver dies because, if he doesn't notice it, he falls asleep without waking up anymore.

In a basic configuration, rebreather systems, in particular semi-closed circuit systems, comprise at least:

one mouthpiece,

one first breathing bag for exhaled breathing gas mixture, in communication with said mouthpiece through a hose, particularly a corrugated hose;

one second breathing bag for the breathing gas mixture from which carbon dioxide has been removed, it also being in communication with the mouthpiece through a hose, particularly a corrugated hose;

one canister removing carbon dioxide from the exhaled breathing gas mixture, which is placed upstream or downstream of a single breathing bag either integrating said first and said second breathing bags or interposed between said first and said second breathing bags;

one tank for a predetermined amount of a gas mixture replenishing the oxygen level in the breathing gas mixture wherein said replenishment gas mixture is stored under pressure as a compressed gas cylinder;

one tube supplying the replenishment gas mixture from the tank to the circuit, a pressure-controlled supply unit supplying a predetermined amount of replenishment gas mixture being provided in the tube, the supply unit being of the servo-controlled type, for example a solenoid valve;

one or more sensors selected among the following sensors or combinations of the following sensors: pressure gauge, oxygen level sensor, carbon dioxide level sensor, depletion sensor for the canister removing carbon dioxide, filling level sensor for the tank with the replenishment gas mixture;

one electronic control unit that receives measurement signals from said sensors and that generates, as a function of said control signals controlling said servo-controlled supply unit, a control signal controlling said servo-controlled supply unit.

Both the closed-circuit rebreathers and the semi-closed-circuit rebreathers are certainly advantageous compared to open systems, as they still allow breathing gas mixture to be saved thereby allowing the duration of dives to be considerably extended while carrying the same breathing gas mixture.

Compared to open breathing systems, wherein the breathing gas mixture supplied by a cylinder is known and constant during the entire dive and is equal to the cylinder filling gas, in the rebreather systems the gas composition in the circuit continuously changes and needs to be precisely monitored during the entire dive. As a result of an electronic measurement of the oxygen, either a purely manual intervention by the diver or a purely electronic intervention by a solenoid valve controlled by a dive computer, or else a mixture of mechanical and electronic action, can be provided. However, a power source is always required to operate the oxygen measurement and the solenoid valve, if any.

It should be noted that, in a semi-closed rebreather, the aid of measurements and mechanical interventions can be theoretically eliminated by providing Nitrox gas through an orifice that defines a fairly high flow with constant flow rate, but this method is very inefficient in using the gas and, furthermore, for the calculation of decompression it is desirable to know the composition of the gas breathed, so that semi-closed systems with a dynamic regulation of the replenishment flow result to be more advantageous. In these systems, however, in case of absence of power and/or electronics malfunction, the current rebreather systems stop the supply of replenishment gas and thus generate a dangerous condition for the user.

In the technical field, especially for sports and recreational purposes, there is therefore the need to further optimize the operation of semi-closed rebreathers in terms of safety.

SUMMARY OF THE INVENTION

The main object of this invention is therefore to improve the state of the art in the field of rebreathers by implementing a system of the so-called rebreather type in which, in case of malfunction of the control electronics and/or absence of electric power, the system automatically takes a safe condition in which supply conditions of the breathing gas mixture are guaranteed which are compatible with user's survival conditions and which make it possible to also perform the various decompression processes for safely surfacing.

In particular, the automatic switching to the safe condition must take place without the need of an active human intervention on a member of the rebreather circuit and thanks to actuators not requiring an electric or electromagnetic energy source.

The object of this invention is a semi-closed rebreather that uses a “normal open” type of solenoid valve to control the flow of replenishment gas supplied to the rebreather circuit by at least one replenishment gas cylinder, i.e. that, in the absence of power, takes the open condition thereby allowing a replenishing gas flow with a maximum flow rate predetermined during the initial design or adjustment step.

In an embodiment, the semi-closed rebreather comprises a recirculation and filtration circuit of the exhaled gas mixture and a circuit to replenish the amount of consumed oxygen comprising a servo-controlled valve that is controlled by a control circuit and is closed if there is an electrical control signal, whereas it takes the completely open condition in the absence of the said electrical control signal.

The invention achieves the above objects by a rebreather type system comprising:

a mouthpiece;

a first breathing bag for exhaled breathing gas mixture in communication with said mouthpiece through a hose, particularly a corrugated hose;

a second breathing bag for the breathing gas mixture from which carbon dioxide has been removed, it also being in communication with the mouthpiece through a hose, particularly a corrugated hose;

a canister removing carbon dioxide from the exhaled breathing gas mixture, which is placed upstream or downstream of a single breathing bag either integrating said first and said second breathing bags or interposed between said first and said second breathing bags when these are separate devices;

a tank for a predetermined amount of a gas mixture replenishing the oxygen level in the breathing gas mixture wherein said replenishment gas mixture is stored at high pressure, i.e. a compressed gas cylinder;

a tube supplying the replenishment gas mixture from the high pressure tank to the circuit, a pressure controlled supply unit supplying a predetermined amount of replenishment gas mixture being provided in the tube, the supply unit being of the servo-controlled type;

one or more sensors selected among the following sensors or combinations of the following sensors: pressure gauge, oxygen level sensor, carbon dioxide level sensor, depletion sensor for the canister removing carbon dioxide, filling level sensor for the tank with the replenishment gas mixture;

an electronic control unit that receives measurement signals from said sensors and that generates a signal controlling the servo-controlled supply unit, the signal being determined as a function of these control signals of said servo-controlled supply unit and wherein

said supply unit comprises a servo-controlled supply valve of the normally open type, which, that is to say, in the absence of an actuation and/or supply control signal, automatically and firmly takes the condition enabling the replenishment gas mixture to be supplied.

According to an embodiment, the electronic control unit executes a control program by means of which said electronic control unit and the sensors are set to detect at least one or more of the following values or combinations of the following values: breathing gas pressure, oxygen level in the first breathing bag and/or second breathing bag, carbon dioxide level in the first breathing bag and/or second breathing bag, depletion level of the carbon dioxide canister, pressure of the replenishment gas in the tank, and which control program sets the control unit to determine the amount of replenishment gas to be supplied in the circuit necessary to replenish a predetermined oxygen level in the breathing gas mixture and to generate control signals for the supply unit corresponding to an actuation of said supply unit for feeding said amount of replenishment gas to be supplied in the circuit, necessary to replenish a predetermined oxygen level in the breathing gas mixture.

Where appropriate, in combination with the control unit a display interface can be provided, displaying one or more measurement data and/or other quantities determined by the one or more sensors or as a function of the values measured by said one or more sensors and/or alphanumeric or graphical messages or information.

Said interface can provide one display monitor controlled by a graphics processing unit that directly executes a graphics display program or is controlled by the control unit in order to be set for the graphic representation displaying one or more measurement data and/or other quantities determined by the one or more sensors or as a function of values measured by said one or more sensors and/or alphanumeric or graphical messages or information.

Still according to an embodiment that can be provided as an alternative or in combination with the previous ones, said electronic control unit can be provided with an interface for the connection with command and/or data input means that can be connected thereto either by cable or wireless connection.

According to a further embodiment variation, the processing unit can be provided with a port for the connection to peripherals storing and/or transmitting programs or to other databases.

According to a further aspect, the electronic control unit executing the control program is a system for controlling the supply of an oxygen-enriched replenishment gas mixture into a rebreather circuit, comprising:

at least setting means to set at least one operating point or setpoint SO₂, corresponding to the target concentration of O₂ in the gas a user can inhale in this circuit, said at least one setpoint (SO₂) being greater than at least one minimum safety value (S_(MIN));

at least detecting means to detect the actual O₂ concentration of this gas that can be inhaled in this circuit;

at least supplying means to supply this oxygen-enriched replenishment mixture; as well as

at least control means for said supplying means;

the control means for the supplying means being controllable based on the volume of the replenishment gas mixture required to add oxygen into the breathing gas mixture to bring the oxygen level in the breathing gas mixture back to the value of the actual O₂ concentration corresponding to at least said setpoint SO₂ determined by the setting means.

According to a further embodiment, a maximum SO₂max setpoint value can be provided, the replenishment gas supplying means being controlled so that the oxygen level in the breathing gas mixture does not exceed said maximum SO₂max setpoint.

Therefore, since a maximum setpoint threshold can be provided, the rebreather control system allows to regulate the oxygen fraction in the breathing gas by controlling the flow rate of the replenishment gas and the opening time of the supplying means, for example of the normally-open type solenoid valve. Depending on both the oxygen fraction of the replenishment gas in the cylinder and the replenishment flow rate, the system can be configured to set a value for the oxygen fraction of the breathing gas mixture and to vary the oxygen fraction of the mixture during diving, in order to further optimize the use of gas. For example, if the replenishment gas in the cylinder is a Nitrox40, by setting a very low flow rate of replenishment gas, an oxygen fraction can be obtained in the breathing gas in the circuit, for example 25% of oxygen in the circuit gas. In other words, starting from a replenishment gas with an oxygen fraction of 40%, as in the case of Nitrox 40, the fraction in the circuit can be reduced to 25% in order to have further efficiency in the use of the gas.

According to a further embodiment variation, a rebreather system according to one or more of the above described embodiments can be provided, in which a second cylinder for decompression is provided. This way, the rebreather system can be optimized for a condition involving very long decompression times.

In this case, a first cylinder containing replenishment gas can be advantageously disconnected from the circuit (for example, the cylinder with 40% oxygen) and a second cylinder with 80-100% oxygen can be connected to the circuit, so that the decompression process can be effectively carried out with gases having high oxygen concentration.

According to a further characteristic, the oxygen-enriched replenishment mixture is a mixture of oxygen and at least one additional physiologically inert gas, such as nitrogen or other gases or mixtures thereof, the oxygen content in the enriched mixture being higher in percentage than the oxygen content in atmospheric air.

According to an exemplary embodiment, the oxygen content of the replenishment mixture can range between 22% and 60%, preferably between 28% and 60%.

In an embodiment variation, the replenishment mixture comprises oxygen content of 40 to 50% with respect to the non-breathable gas component such as nitrogen, other gases or mixtures thereof.

As evident, thanks to the valve of the normally open type, in condition of malfunction of the electronics of the rebreather system and in particular of absence of electric power, the replenishment mixture freely flows into the circuit with a flow sufficient to cover the needs of an emergency situation.

Still according to an advantageous embodiment, the electronic control unit is provided with a functional diagnostics automatic sub-system that, in case of detection of one or more non-correct operating conditions of the electronic unit and/or of one or more peripherals connected to said electronic unit, sets the supply valve in the open condition by automatically stopping irreversibly or vitally the input of the control signal of the supply valve that maintains it in the closed condition.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects of the present invention will be more apparent from the following description of some exemplary embodiments depicted in the accompanying drawings, wherein:

FIG. 1 shows a schematic view of a circuit of a breathing system of the rebreather type and of semi-closed-circuit type.

FIG. 2 shows a flow diagram of an embodiment of the device according to the invention, wherein the emergency functional mode is activated by the control unit that at least partially works based on a diagnostic analysis.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In FIG. 1 a semi-closed-circuit rebreather system is schematically shown. The user inhales and exhales through a mouthpiece 10 a breathing gas mixture contained in a circuit. The mouthpiece 10 has a connecting branch to a first breathing bag 20 into which exhaled air is injected. A non-return valve 21, during the inhalations, prevents the previously exhaled breathing gas mixture from being inhaled from the first breathing bag before being treated in the carbon dioxide removal unit 30 and before the oxygen content consumed during the previous inhalation/exhalation is replenished.

The output of the first breathing bag 20 communicates with the canister for removing carbon dioxide and the gas mixture, from which carbon dioxide has been removed, is supplied to a second breathing bag 40.

A tube 60 to supply a gas mixture replenishing the oxygen level in the breathing gas connects the second breathing bag 40 with a cylinder 50 containing a predetermined amount of said replenishment mixture at a given pressure.

A pressure reducer 70 is provided in the replenishment gas mixture supply tube 60 in order to control the pressure of the replenishment gas supplied into the breathing bag 40, whereas the supply of the replenishment gas mixture to the second breathing bag is controlled by means of a solenoid valve 80.

The second breathing bag 40 communicates with the mouthpiece 10 by means of a non-return valve 41 which prevents the exhaled gas mixture flow from being supplied also to the second breathing bag 40.

The system is controlled by a control unit denoted by 90. The control unit 90 generates the control signals of the supply solenoid valve 80 based on the measurement signals of the various sensors that are provided in the system and that are not depicted separately from each other but cumulatively by the boxes 100, in order not to complicate the figure.

Different sensor combinations can be provided for the measurement of different quantities.

In a minimum configuration, the system comprises at least one sensor for the oxygen concentration in the breathing gas mixture, which can be used to monitor the oxygen level in the breathing gas mixture and to determine the amount of replenishment mixture required to compensate for oxygen consumption due to the respiratory cycle.

Two sensors are preferably provided for measuring the oxygen concentration:

a sensor for measuring the ambient pressure;

an sensor for measuring the oxygen partial pressure;

and the oxygen fraction, which is the measure of interest in a semi-closed rebreather, can be obtained from these two measurements.

According to an improvement, at least one sensor of the carbon dioxide concentration in the breathing gas mixture, at least one detector of the saturation level of the canister for removing carbon dioxide, at least one sensor of pressure and/or the charge level of the replenishment gas cylinder, can be further provided.

This sensor or these are optional sensors, as the canister capacity is more than satisfactorily controlled by changing the soda lime at the right frequency. On the contrary, the measurement of the pressure in the cylinder is intended to warn the diver when the gas is almost used up.

Therefore, the improvement obtained by checking both the level of carbon dioxide in the breathing gas mixture and the duration of the canister removing carbon dioxide from the breathing gas mixture to monitor the remaining life of the canister and thus the time limits of the dive, goes beyond the performance of the control system in the basic configuration.

Similarly, the amount of replenishment mixture and the dive time can be checked with reference to the possibility of compensating for the oxygen consumption in the breathing gas mixture.

Measurements of additional quantities can also be provided that are further redundant with respect to the minimum configuration and can help to increase the level of reliability of the system control by cross-checking measurement values. For example, the oxygen level can be measured both in the exhalation branch connecting the mouthpiece 10 to the first breathing bag 20 and in the inhalation branch connecting the second breathing bag to the mouthpiece 10 or else in the first and second breathing bags, respectively.

The control unit 90 can consist of either analogue or digital hardware.

In an embodiment, an algorithm for calculating the amount of replenishment mixture to be supplied into the circuit to compensate for physiological consumption of oxygen from the breathing gas mixture can be permanently implemented in the hardware as well as, as a result, the control signals of the solenoid valve 80 depending on the measurement signals detected by one or more sensors according to any of the sensor configurations described above.

On the other side, a preferred embodiment variation provides that the hardware consists of a processor unit equipped with a processor, at least one storage unit, at least one working storage and at least one program loading port in which the calculation algorithm is encoded as instructions executable by the processor to determine the amount of replenishment mixture to be supplied into the circuit to compensate for the physiological consumption of oxygen from the breathing gas mixture and to determine, as a result, the control signals of the solenoid valve 80 depending on the measurement signals detected by one or more sensors under any of the above-described configurations.

According to a further improvement, the control system comprises at least one communication port to communicate with one or more different types of data and/or command input interfaces globally denoted by 91.

Through these interfaces it is possible to set the system operating conditions, for example parameters for configuring the calculation algorithm and/or threshold values for the level of oxygen content in the breathing gas mixture and/or parameters for setting the canister functions and parameters for setting additional peripherals which may also be connected to the control unit 90, such as graphics interfaces in which the appearance of the interface itself, in relation to the available tools and menus or information and/or the appearance of the representation of information about the operative state and the expected life of the canister and/or of the replenishment gas mixture, as well as aspects relating to the planning of the dive and decompression times, can be changed in appearance in order to facilitate user understanding.

According to a further feature, the control unit 90 can comprise a display monitor 92 connected to a port of the control unit itself. The display can also be a touch-screen.

According to another embodiment, the control unit 90 can be equipped with one or more wireless communication ports 93 to communicate with any type of device or peripheral and it can also be integrated with means transmitting identification and/or communication signals to other control units for communicating with a remote control station and/or other units of other users.

Thanks to the data and/or command input interface 91, at least one operating point or setpoint (SO₂) can be stored, corresponding to an O₂ concentration to be achieved, in use, in the breathing gas mixture, for example in the second breathing bag 40 or in the branch connecting the latter to the mouthpiece 10.

The sensors 100 measuring the O₂ concentration actually present in the breathing gas mixture can be provided both in the first and the second breathing bags or in the branches connected thereto which lead to the mouthpiece and the values determined by these sensors are used to determine the amount of replenishment gas mixture to be introduced in the second breathing bag 40 in order to bring the oxygen concentration in the breathing gas mixture back to the value of the predetermined setpoint.

The data calculated by the processor unit constituting the control unit 90 is turned into a command for the valve 80 by the control unit itself.

The valve 80 is of the normally open type, i.e. a servo-controlled valve that, in the absence of a control signal, takes the completely open condition, while requiring a control signal to take the closed condition. This means, therefore, that the control signal mentioned above also includes the condition of absence of a signal. When the electronic control unit 90 detects the need to supply a predetermined amount of replenishment mixture into the breathing bag 40, it stops the input signal to the valve 80 in order to cause the latter to open for a predetermined time, which is defined by the amount per time unit of replenishment gas mixture passing through the aperture of the valve 80 and by the oxygen concentration in the replenishment gas mixture.

If the oxygen concentration in the breathing gas mixture is at the set level, the valve 80 is kept closed and a corresponding control signal is provided thereto by the control unit.

This configuration has the advantage that in the absence of power or in conditions where the available power is low, the valve 80 takes the open condition and therefore allows the replenishment mixture to freely pass into the breathing bag 40.

The mechanical pressure reducer 70 ensures that the pressure is at a value controlled and set by itself. In addition, there is an overpressure valve in the circuit which expels an amount of breathing gas mixture when the pressure exceeds a certain maximum set value.

In FIG. 1 this valve is denoted by 110.

At the same time, the overpressure valve 110 is the system provided in semi-closed circuit rebreathers to discharge from the circuit a part of the exhaled breathing gas mixture corresponding to the amount of replenishment gas mixture supplied into the breathing bag 40.

According to another embodiment, the flow of the replenishment gas mixture in the open condition of the servo-controlled supply valve 80 can be controlled. In this case, a flow regulation unit 120 can be provided, which can be adjusted with a fixed or adjustable passage aperture and which is placed in series with the passage aperture of the valve.

The flow regulation unit for regulating the flow of gas mixture replenishing the oxygen level may either consist of a unit separated from the valve as shown in the figure, or it may be integrated therein.

Adjustment can be carried out only once during manufacture and can be adaptable during maintenance work, or it can be carried out by means of actuators also controlled by the control unit 90.

Advantageously, when actuators can be used to change the adjustment of the passage aperture of the flow regulator 120, in case of lack of power supply to the actuators, the setting is preferably kept stable, so that to operate the actuators, an active action is required in order to change the setting.

In an embodiment, the flow regulator means 120 are set to supply a constant flow of replenishment mixture with a preferably relatively high flow rate, optionally between 15 and 25 l/min.

According to yet another embodiment of the invention, a control unit having a program of diagnostic analysis loaded therein can be provided, the control unit executing the program itself for example cyclically and actively by controlling the open condition of at least the valve 80 upon detection of a condition of potential failure or partial malfunction able to compromise the proper replenishment of the breathing gas mixture, not providing the control signal that maintains the valve in the closed condition. This way, thanks to the active intervention of the control unit on the system, the user can be prevented from being in dangerous conditions without realizing it, due to malfunctions that progressively modify the oxygen concentration with respect to the one set as set point, or from performing not-recommended operations.

The flow diagram in FIG. 2 shows a diagnostic cycle described above.

The diagnostics program is activated at step 200. This is done as general setting of the control unit 90.

The diagnostic cycle is activated by following the repetition times of the diagnostic cycles at step 210.

According to a preferred embodiment, the diagnostic program carries out a checking test of various functionalities. Compared to the flow diagram shown, only some of the functionalities shown in FIG. 2 can be provided.

In particular, in this example showing the most complete diagnostic system at step 220, a functional check of the processor is carried out. The memory operation is checked at step 230. The functionality of the sensors is checked at step 240. In step 250, the diagnostic program calculates the deviation between the set oxygen level and the actually measured oxygen level in the rebreather circuit. This step can also comprise a comparison of the deviation values with the previous cycles and therefore the possibility to check a drift of the actual oxygen concentration value which may be caused by a progressive loss of control unit and/or sensor functionalities.

As depicted at step 260, it is also possible to perform functional tests of the carbon dioxide removing canister, which may consist both in detecting the canister conditions and in determining the concentration of carbon dioxide in the breathing gas mixture.

Step 270 analyses the data relative to the checks and, based on a comparison with either a risk determination table or an algorithm for calculating a risk index, depending on the test results expressed with numerical evaluations, it is determined whether the system functionality is sufficient to guarantee the continuation of the dive under normal conditions or the system is undergoing a malfunction and it is necessary to switch to the emergency operating mode.

In the first case, the next cycle is executed after the time interval provided in a sequence of diagnostic checking cycles. In the second case, step 280 reports the transition to the emergency condition and step 290 essentially activates this condition by stopping the input to the replenishment mixture supply valve of the signal that maintains the valve itself in the closed condition and thus permanently bringing the latter to the fixed open condition.

Other steps can be carried out according to one or more of the embodiment variations described above.

At step 291, when the electronic control unit 90 and at least some of the peripherals 91, 92, 93 and at least some of the sensors 100 are operating, the electronic control unit may continue to operate by carrying out only the functions it properly operates according to the previously performed checks.

Advantageously, the input of the closing control signal to the replenishment gas mixture supply valve is blocked so that the same blocking condition is automatically irreversible, i.e. it occurs in vital mode.

In this case, for example, in the electric line connecting the actuator of the supply valve to the control unit 90 there may be a relay of the type with normally open contacts and, in the absence of a signal, it may take a stable and non-recoverable opening appearance. Therefore, the control signal that maintains the supply valve in closed condition can be input to the latter only if the rebreather maintenance personnel perform a manual reset once the system functionality tests have been carried out.

Advantageously, according to an embodiment, the results of the various self-diagnosis cycles performed by the control unit, i.e. by the self-diagnosis subsystem thereof, can be stored in a memory or in a dedicated memory area and can be accessed and/or downloaded by the service personnel to be remotely analyzed in order to identify the causes that led to the activation of the emergency operating mode. Thus, the cause can then be identified and removed and the vital relay or switch 140 can be returned manually to the closed condition of the line connecting to the actuator of the supply valve 80.

Still according to a further feature, it is possible to provide an emergency breathing loop comprising a diving regulator 130 that is directly connected through a manual valve to the replenishment mixture cylinder, downstream of the pressure regulator and thus forming an open breathing system of the traditional type that can be used alternatively to the rebreather circuit. This involves additional safety especially when, for example, the carbon dioxide filtering function is no longer available due to a malfunction of the canister 30.

According to an embodiment, an alternative diving regulator 130 is provided and connected to the cylinder 50 through the reducer 70.

While the invention has been described in connection with the above described embodiments, it is not intended to limit the scope of the invention to the particular forms set forth, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be included within the scope of the invention. Further, the scope of the present invention fully encompasses other embodiments that may become obvious to those skilled in the art and the scope of the present invention is limited only by the appended claims. 

The invention claimed is:
 1. A rebreather system comprising: a mouthpiece; a first breathing bag for exhaled breathing gas mixture in communication with said mouthpiece through a hose; a second breathing bag for the exhaled breathing gas mixture from which carbon dioxide has been removed, said second breathing bag also being in communication with the mouthpiece through a hose; a canister removing the carbon dioxide from the exhaled breathing gas mixture interposed between said first and said second breathing bags; a tank for a predetermined amount of a replenishment gas mixture replenishing oxygen level in the breathing gas mixture, where said replenishment gas mixture is stored at high pressure; a tube supplying the replenishment gas mixture from the tank to the second breathing bag, a pressure controlled supply unit supplying a predetermined amount of the replenishment gas mixture being provided in said tube, said supply unit being servo-controlled; one or more sensors or combination of sensors selected among the group consisting of: pressure gauge sensor, oxygen level sensor, carbon dioxide level sensor, depletion sensor for the canister removing carbon dioxide, and filling level sensor for the tank with the replenishment gas mixture; and an electronic control unit that receives measurement signals from said one or more sensors or combination of sensors and that generates, as a function thereof, signals controlling said supply unit, wherein said supply unit comprises a servo-controlled supply valve of a normally open type, said servo-controlled supply valve, in absence of a control actuation signal, automatically and firmly taking a condition enabling the replenishment gas mixture to be supplied.
 2. The rebreather system according to claim 1, further comprising a flow rate regulator for a flow of replenishment gas mixture replenishing an oxygen concentration level in the breathing gas mixture.
 3. The rebreather system according to claim 1, wherein the electronic control unit is a the processor and executes a control program, by which said electronic control unit and the one or more sensors or combination of sensors are set to detect at least one or more of the following values or combinations of the following values: breathing gas pressure, oxygen level in one or both of the first breathing bag or second breathing bag, carbon dioxide level in the first breathing bag and/or second breathing bag, depletion level of the carbon dioxide canister, level of the replenishment gas mixture in the tank, or pressure of the replenishment gas in the tank, and wherein the control program sets the control unit to determine the amount of the replenishment gas mixture be supplied in a circuit necessary to replenish a predetermined oxygen level in the breathing gas mixture and to generate control signals for the supply unit corresponding to an actuation of said supply unit for feeding said amount of the replenishment gas to be supplied in the circuit necessary to replenish a predetermined oxygen level in the breathing gas mixture.
 4. The rebreather system according to claim 1, wherein, in combination with the electronic control unit, an interface is provided displaying one or more measurement data and/or other quantities determined by the one or more sensors or combination of sensors, or as a function of values measured by said one or more sensors and/or alphanumeric or graphical messages or information.
 5. The rebreather system according to claim 4, wherein said interface comprises one display monitor controlled by a graphics processing unit that directly executes a graphics display program or is controlled by the control unit to be set for a graphic representation displaying one or more measurement data and/or other quantities determined by the one or more sensors or combination of sensors, or as a function of values measured by one or more of said one or more sensors or combination of sensors, or said alphanumeric or graphical messages or information.
 6. The rebreather system according to claim 1, wherein said electronic control unit is provided as an alternative or in combination with an interface for connection with a command and/or data input system that is connected thereto both by cable or wireless connection and/or with a port for the connection to peripherals storing and/or transmitting programs or other data libraries.
 7. The rebreather system according to claim 1, further comprising an exhaust valve for a predetermined amount of the breathing gas mixture for maintaining a predetermined pressure of the breathing gas mixture.
 8. The rebreather system according to claim 7, wherein said exhaust valve is configured to be activated or deactivated by a command of the electronic control unit.
 9. The rebreather system according to claim 1, wherein the electronic control unit is provided with a functional diagnostics automatic sub-system, which, in case of detection of one or more non-correct operating conditions of the electronic control unit and/or of one or more peripherals connected to said electronic control unit sets the supply valve in an opening condition stopping automatically irreversibly or vitally an input of the control signal of the supply valve that maintains the supply valve in a closed condition.
 10. The rebreather system according to claim 1, wherein the gas mixture replenishing oxygen is a mixture of oxygen and of at least one additional physiologically inert gas, a content of the oxygen in said mixture ranging from 22% to 60% with respect to a non-breathable gas component.
 11. The rebreather system according to claim 1, further comprising at least one second tank for a replenishment gas having an oxygen content higher than 60%, said second tank being connectable to the breathing loop of the rebreather alternately to the a tank for a predetermined amount of a replenishment gas mixture replenishing oxygen level in the breathing gas mixture. 